Bonsai caring should not be taken lightly. There are many different types of trees with completely different ways to care for them.
Before you select a bonsai, get full information of the type of tree and specific way of caring. This will be more important than how beautiful the tree looks as you will need to seriously consider where you live, local weather, you everyday schedule and many more points.
As Wazakura sometime says in their post, bonsais are living beings. Sounds obvious but is easy to forget.
Talking about obvious, but it is easy to miss that, due to the small size of the planter, soil does not stay wet and with enough nutrients for long. Also some types of soil like clay do not absorb water well.
So, watering often is a must. It needs to be avoided to let the soil dry or the tree can soon follow.
->Because each tree is different, get the recommended times of watering by the supplier. Even the general rule may change based on the season and weather.
->This is why your every day schedule is important to consider. If you are not able to water the tree in time, it may be better to consider a different one.
Outdoor vs. Indoor:
Getting an outdoor bonsai but your city apartment barely have a balcony with decent sunlight? Maybe an indoor one is better?
Outdoor trees will start to get yellowish if kept indoor for too long. Need light and good ventilation.
->Also, avoid the air conditioner hitting the tree directly.
Again, an obvious one, but if someone thinks that a 30 min exposure to sunlight is good enough for the bonsai, then it is worth saying that, in general, all bonsai needs a lot of light every day.
->Booth outdoor and indoor will need plenty of light so choose the placing accordingly.
You are probably looking to try your bonsai tools and start arranging the bonsai as you like. Once again, the bonsai is a living thing; doing lots of cuts and changes put the tree under a lot of stress and could very well be the end of the tree.
->Let the tree grow and be reasonable with the cuts. This require patience.